In the coming year, work will proceed along two main lines. The study to determine the mechanism of muscular contraction will extend from the steady to the non-steady state. In addition to looking at the muscle cross bridge interaction during an isometric tetanus, we will look at the interaction during isotonic shortening, during isometric redevelopment of force and during situations of incomplete fiber activation. Work on the study of cardiac excitability will be directed toward extending our model for the passive Purkinje fiber to the active fiber. We will then explore the role of geometry as well as other variables in influencing cardiac excitability.